Applicant's disclosure is directed generally towards a wireless communications network for determining whether a signal from a mobile appliance is operated on by a repeater thereby further enabling a determination of the location of mobile appliances.
The use of wireless communication devices such as telephones, pagers, personal digital assistants, laptop computers, etc., hereinafter referred to collectively as “mobile appliances,” has become prevalent in today's society. Recently, at the urging of public safety groups, there has been increased interest in technology which can determine the geographic position or geolocate a mobile appliance in certain circumstances. For example, the Federal Communication Commission (FCC) has issued a geolocation mandate for providers of wireless telephone communication services that puts in place a schedule and an accuracy standard under which the providers of wireless communications must implement geolocation technology for wireless telephones when used to make a 911 emergency telephone call (FCC 94-102 E911).
In addition to E911 emergency related issues, wireless telecommunications providers are developing location-enabled services for their subscribers including roadside assistance, turn-by-turn driving directions, concierge services, location-specific billing rates and location-specific advertising.
To support FCC E911 rules to locate wireless 911 callers, as well as the location enabled services, the providers of wireless communication services are installing mobile appliance location capabilities into their networks. In operation, network overlay location systems take measurements on RF transmissions from mobile appliances at base station locations surrounding the mobile appliance, and estimate the location of the mobile appliance with respect to the base stations. Because the geographic location of the base stations is known, the determination of the location of the mobile appliance with respect to the base station permits the geographic location of the mobile appliance to be determined. The RF measurements of the transmitted signal at the base stations can include time of arrival, angle of arrival, signal power, or unique/repeatable radio propagation path (radio fingerprinting) derivable features. In addition, the geolocation systems can also use collateral information, e.g., information other than that derived for the RF measurement to assist in the geolocation of the mobile appliance, i.e., location of roads, dead-reckoning, topography, map matching, etc.
In a network-based geolocation system, the mobile appliance to be located is typically identified and radio channel assignments determined by (a) monitoring the control information transmitted on radio channel for telephone calls being placed by the mobile appliance or on a wireline interface to detect calls of interest, i.e., 911, (b) producing a location request provided by a non-mobile appliance source, i.e., an enhanced services provider. Once a mobile appliance to be located has been identified and radio channel assignments determined, the location determining system is first tasked to determine the geolocation of the mobile appliance and then directed to report the determined position to the requesting entity or enhanced services provider.
The monitoring of the RF transmissions from the mobile appliance or wireline interfaces to identify calls of interest is known as “tipping”, and generally involves recognizing a call of interest being made from a mobile appliance and collecting the call setup information. Once the mobile appliance is identified and the call setup information is collected, the location determining system can be tasked to geolocate the mobile appliance.
FIG. 1 shows a conventional mobile-appliance communication system having base stations 10 a-c for communicating with a mobile appliance 20. Each base station 10 contains signal processing equipment and an antenna for transmitting to and receiving signals from the mobile appliance 20 as well as other base stations. A Base Station Controller (“BSC”) and/or Mobile Switching Center (“MSC”) 45 typically is connected to each base station 10 through a wireline connection 41. A mobile appliance location determining sensor 30, i.e., wireless location sensor (“WLS”), may be positioned at some or all of the base stations 10 to determine the location of mobile appliance 20 within the signal coverage area of the communication system.
A network overlay system is generally composed of two main components, one that resides at the base station that makes measurements on the RF signal emanating from the wireless device, the WLS 30, and one that resides at the mobile switch that tasks the WLS groups to collect data and then uses the data to compute a location estimate, the Geolocation Control System (“GCS”) 50. In the normal course of operation, the GCS is tasked by an outside entity, e.g., the Mobile Positioning Center (“MPC”) 40, to generate a location estimate on a particular mobile appliance. The tasking is accompanied by information on the mobile of interest including the serving base station and sector for the call and the RF channel (frequency, time slot, CDMA code, etc.) being used by the wireless communications network to complete the wireless connection. Once the GCS receives this tasking, it tasks a set of WLS units to make measurement on the RF emission of the mobile based on the serving sector. The WLS units make the measurements, and report the measurements to the GCS. The GCS then computes a location estimate using a mathematical or data matching algorithm. Alternatively, control signaling on RF or wireline interfaces used to set up calls in the wireless network can be scanned to detect the placement of a call of interest. The signaling that occurs on the RF control channel can be used to determine location, or call setup/channel assignment parameters can be extracted from the control messaging to determine which traffic channel to use for location related measurements.
Network overlay location systems typically locate a mobile appliance on the traffic channels of a wireless network. The system typically uses sensors employing techniques of Time Difference of Arrival (“TDOA”) supplemented with Angle of Arrival (“AOA”) in some cases to perform a multi-site location computation. The traffic channel assignment information is provided through a separate process, with one option being a wireline interface providing MOBINFO (IS-41 Mobile Information) parameters passed by the Mobile Positioning Center as part of the GPOSREQ (J-STD-036 Geolocation Position Request) message from the MPC to the GCS 50.
To meet the ever growing demand for mobile communication, wireless communication systems deploy repeater stations to expand range and concentration of coverage. In FIG. 1, a repeater 50a, associated with base station 10a, is located to extend the coverage area to encompass the back side of the mountain 1. The repeater 50b, associated with base station 10c, is mounted on a building and is used to provide service within the building 2.
Repeaters typically fall into two categories: (1) non-translating, also known as wideband, and (2) translating, also known as narrowband. As shown in FIG. 2a, a non-translating repeater 250 simply passes the forward Ff1 and reverse Rf1 frequencies from the base station 210 and mobile appliance 220 respectively to and from the repeater coverage location. Often wideband repeaters are “in-building” or serve limited coverage areas. While the description of non-translating repeaters above and translating repeaters below are described in reference to frequency, their operation can equally be described in terms of channels, and the use of the term frequency should not be construed to limit the scope of the present disclosed subject matter.
A translating repeater assigns the mobile to a different traffic channel unbeknownst to the base station, mobile switch, MPC, and the base station controller. As shown in FIG. 2b, the translating repeater uses the base station traffic channel Rf1 for repeater 250 to base station 210 communication while the mobile appliance 220 utilizes a separate frequency Rf2 for mobile to repeater communications. Translating repeaters act similarly in the forward direction using Ff1 from the base station 210 to the repeater station 250 and Ff2 from the repeater station 250 to the mobile appliance 220. In both cases, the existence of the repeater is usually transparent to the network.
The function of the repeater station can be assumed to be equivalent to converting all signals in some received bandwidth from a Radio Frequency (RF) to some Intermediate Frequency (IF). The IF signal bandwidth is then up-converted by suitably frequency shifting this bandwidth while concurrently applying both amplification and a fixed delay to the signals.
For example, let the set of signals transmitted by N mobiles in the repeaters input bandwidth be denoted by
            S      ⁡              (        t        )              =                  ∑                  k          =          1                N            ⁢                          ⁢                        a          ⁡                      (            k            )                          ⁢                  x          ⁡                      (                          k              ,              t                        )                          ⁢                  sin          ⁡                      (            wt            )                                ,where the signal from a given mobile is denoted by x(k, t). The signal x(k, t) is contained in the repeater bandwidth and w is the angular frequency center of the RF bandwidth. The repeater downshifts the aggregate signal to generate
            D      ⁡              (        t        )              =                  ∑                  k          =          1                N            ⁢                          ⁢                        a          ⁡                      (            k            )                          ⁢                  x          ⁡                      (                          k              ,              t                        )                          ⁢                  sin          ⁡                      (            vt            )                                ,in which v is now representative of the center of the IF bandwidth. The entire signal D(t) is now converted back to RF by operations that are equivalent to forming the signal
            R      ⁡              (                  t          +          T                )              =                  G        ⁢                              ∑                          k              =              1                        N                    ⁢                                          ⁢                                    a              ⁡                              (                k                )                                      ⁢                          x              ⁡                              (                                  k                  ,                  t                                )                                      ⁢                          sin              ⁡                              (                vt                )                                      ⁢                          cos              ⁡                              (                                  wt                  -                  vt                                )                                                        +              G        ⁢                              ∑                          k              =              1                        N                    ⁢                                          ⁢                                    a              ⁡                              (                k                )                                      ⁢                          x              ⁡                              (                                  k                  ,                  t                                )                                      ⁢                          cos              ⁡                              (                vt                )                                      ⁢                          sin              ⁡                              (                                  wt                  -                  vt                                )                                                          ,in which G is the repeater gain. The last equation can be written in a more convenient mathematical manner by noting that R(t) can be derived from D(t) by writing it as R(t+T)=Re{G exp(j(w−v)tI(t))}, where G exp(f(w−v)t) is the complex representation of the multiplicative signal introduced by the repeater on the downshifted signal bandwidth and I(t) is the complex representation of D(t).
Essentially, the function of the repeater is to convert the RF signal to an IF signal, delay and amplify that IF signal, up-convert the signal back to RF, and transmit the signal. This is true for both translating and non-translating repeaters.
Repeaters typically communicate with the host base station via an RF link as shown in FIG. 3 between base station 310 and repeater 350a. This connection allows remote operation of the repeater without physical ties back to the host base station, which is particularly advantageous in rugged or other areas where laying lines are difficult or costly. Some repeaters, generally non-translating repeaters, use a fiber optic or copper wire “tether” instead of an RF link to communicate with the host base station as shown in FIG. 3, where base station 310 is connected to repeater station 350b by tether 351. RF signals are placed onto the tether at the repeater and then summed into the normal base station antenna path at the antenna feed interface 311 at the host base station. After integration into the normal base station antenna path, the signal from the repeater is indistinguishable to the base station regarding its origin (e.g., from the base station antennas or from a tether). In this tether architecture as well, the host base station has no knowledge of the repeater's existence or that a call is being served by the repeater.
Neither the base station nor the switch knows that a repeater is serving a call. Therefore the GPOSREQ information from the MPC which, in part, originates from the switch, is not able to alert the Geolocation system that a repeater is in use. When a prior art network overlay location system attempts to locate a mobile being served by a repeater without knowing that a repeater is serving the mobile, a number of alternatives may occur. The location system may locate the mobile based on receiving only RF signals directly from the mobile at a sufficient number of sites to locate the mobile. This alternative is the same as if the repeater was not involved from the standpoint of the location system. Another alternative is that the location system would receive signals from the repeater backhaul link antenna and produce a location. Thus, the location of the repeater antenna (rather than the mobile) would be the “worst case” geolocation computed location.
For example, a repeater installed as an in-building distribution system would use indoor antennas to communicate with the indoor handsets and an outdoor antenna to communicate with the host base station. If the geolocation system were unable to locate the mobile itself, the location of the outdoor antenna (the repeater) would be used. Since this is the location of the building housing the mobile, this is a much better location estimate than Phase I cell-sector information and is often compliant within the FCC accuracy mandate over the given network. A Phase I system typically does not know of repeater existence and uses the host cell's cell-sector information for location. While acceptable in some cases, as identified above, using the location of repeater 50a in FIG. 1, would be of little use. In the case where the location system receives the RF signal from a mixed set of sources (some from the mobile and some from the repeater backhaul antenna), an erroneous location estimate can be generated. If only one signal is received, its path (either through the repeater or direct propagation) must be determined to calculate at an accurate location estimate. If the wrong assumption is made, the large delay through the repeater wrongly applied can add large errors to the TDOA surfaces and intersection points. In the case where the location system does not receive RF at sufficient WLS sites to generate a location estimate due to the effects of the repeater action or transmitted power of the mobile or directionality of the repeated signal from the repeater backhaul antenna, no location estimates will be reported.
Therefore, there is a need in the prior art for a network overlay geolocation system and method of operation in a host wireless communication system that provides accurate geolocation of mobiles served by repeater stations. In order to accomplish this, there is a need to overcome the deficiencies in the prior art by employing a novel geolocation system and method that is capable of identifying when a mobile's signal is being received via a repeater.
In view of this need, it is an object of the disclosed subject matter to obviate the deficiencies in the prior art and present an improved method for determining the location of a mobile appliance in a wireless communication system with base stations and a repeater for communicating with the mobile appliance.
It is also an object of the disclosed subject matter to present a method for determining whether a signal is received directly from the mobile or from a repeater in the communication network.
These objects and other advantages of the disclosed subject matter will be readily apparent to one skilled in the art to which the disclosure pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.